French patent application FR-2,774,454 describes a water heating device comprising a firing chamber with a primary air inlet arranged below a combustion chamber. The firing chamber is equipped with a means intended to initiate the spontaneous combustion of the heterogeneous and preferably greasy waste. However, such a furnace, specifically suited for heterogeneous waste, notably has the drawback of requiring great care in handling the waste and of involving uncertain combustion regulation.
Organic waste such as meat flour or palmiped viscera poses difficult combustion problems because, once dried, the volatile matter content of these products is too high to allow direct burning in a conventional incinerator (grate destruction due to locally high temperatures). In a conventional furnace, the hot zones could be eliminated by using wet waste (50% water or more), but the geometry of these furnaces is not suited to allow correct recovery of all the radiation of the flames present in the combustion chamber, to warm the waste up and to efficiently eliminate the water contained therein. Spontaneous combustion is then no longer provided, which sooner or later results in a combustion stop.